The kinetics of the reaction of superoxide radical with Fe(III) complexes of EDTA, DETAPAC and HEDTA

Abstract

To gain an understanding of the mechanism by which the hydroxyl free radical can arise in superoxide generating systems and learn how different chelaters of iron can inhibit this reaction, a pulse radiolysis kinetic study of the reaction of O;-with Fe(III)EDTA, Fe(III)HEDTA and Fe(III)DETAPAC (or DTPA) was undertaken. Superoxide reacts readily with Fe(III)EDTA and Fe(III)HEDTA with a pH-dependent second-order rate constant having values of 1.9 x lo6 M-l. s-' and 7.6 x 16 M-'. s-' at pH 7, respectively. However, the rate constant for the reaction of O;-with Fe(III)DETAPAC was found to be much slower, the upper limit for the rate constant being 104 M-l. s-l. These results in conjunction with spin-trapping experiments with Fe(II)EDTA, Fe(II)HEDTA, Fe(II)DETAPAC and Hz02 suggests that DETAPAC inhibits the formation of 'OH by slowing the reduction of Fe(II1) to Fe(I1) and not by inhibiting the Fenton reaction.

NO removal in continuous BioDeNOx reactors: Fe(II)EDTA2− regeneration, biomass growth, and EDTA degradation

“…7A), in contrast to the anaerobic batch incubations (Fig. 7B) catalyzed Haber-Weiss reaction (Buettner et al, 1983;Sutton, 1985;Welch et al, 2002):…”

Effects of Buffer Solutions and Chelators on the Generation of Hydroxyl Radical and the Lipid Peroxidation in the Fenton Reaction System.

“…For example, EDTA-Fe(II) and diethylenetriamine pentaacetic acid (DETAPAC)-Fe(II) complexes react readily with H2O2 to form •OH [5][6][7][8], but the Fenton reaction is prevented by the chelation of iron by phytate [9]. Meanwhile, DETAPAC-Fe(III) is hardly reduced by 02, , so that DETAPAC-Fe is believed not to be a good catalyst of the Haber-Weiss cycle, and fails to support • OH generation [10]. Another report suggested the requirement for at least one coordination site of iron that is open or occupied by readily dissociable ligand such as water for catalytic activity; EDTAFe, nitrilotriacetic acid (NTA)-Fe, ADP-Fe, etc.…”

Importance of Iron Complexation for Fenton-Mediated Hydroxyl Radical Production at Circumneutral pH

“…For (Buettner et al, 1983) and ≈10 3 M −1 s −1 (Bolann et al, 1992), whereas Fe(II)DTPA is readily oxidized, with k 7 = 2 × 10 7 M −1 s −1 (Butler and Halliwell, 1982) (Ilan and Czapski, 1977;Bull et al, 1982Bull et al, , 1983, with k 7 = 2 × 10 6 M −1 s −1 appropriate under the conditions of this study (see Supplementary Material Section 6 for further discussion). Unlike DTPA, Fe(III) complexed by EDTA is readily reduced by O…”

“…[o] Garg et al (2007) give 800 M −1 s −1 , Rose and Waite (2005) give 9 × 10 4, M −1 s −1 ; see text for discussion. [p] Reaction considered slow (<10 4 M −1 s −1 , Buettner et al (1983)) and as such was not included.…”